Such devices are primarily used in automobile production to transport motor vehicle parts or the motor vehicle to be produced in its respective stage of production between the individual assembly points. To this end a frame is usually able to be moved horizontally on a rail, the height of a crossmember can be adjusted via the stay hinged onto it using lifting gear arranged on the frame, with the conducting of the stays being selected so that sideways swinging movements are damped.
The load, especially if it is a motor vehicle provided for assembly, should be suspended as stably as possible; this is because many assembly processes are fully automated, which demands precise positioning of the carrying apparatus, which in turn demands the most stable possible suspension of the load on the crossmember. Since simple cable drives with vertical carrying cables are not suitable to both secure the load and prevent it swinging in all directions, articulated arms or struts are used in addition to the cable stays, hinged on one side on the frame and on the other side on the crossmember and which stabilize the load without preventing the raising and lowering movements.
The numerous known solutions are complex, heavy and expensive. German Patent Application DE 36 36 459 A1 thus describes a generic device for guiding a load which similarly consists of a movable frame to which a crossmember with height adjustment is linked. To avoid swinging movements of the load in and against the direction of movement of the frame, two intersecting telescopic struts of adjustable length are provided between frame and crossmember, said struts having articulated joints in their end regions to attach them to the crossmember on one side and the frame on the other, and which serve to accept the forces arising in the direction of movement of the carrier device. In this solution the load is lifted using the lifting stays, which are hinged in the corner areas of the crossmember and are routed via deflection pulleys in the corner areas of the frame to central lifting gear arranged on the frame. For synchronization of the extension and retraction movement of the telescopic struts, these are stabilized and synchronized by a network of cable stays, with deflection pulleys being provided at the free ends of the extendable telescopic parts of the telescopic arms via which the stay connected to the fixed part of the telescopic struts, after deflection at the rear end of the extendable telescopic struts, is routed to the other telescopic strut in each case and is attached there. Since the stays are routed in a symmetrical mirror image, each stay is stressed for tension in a direction opposite to that of the other stay, whereby a largely swing-free movement of the load can be achieved. This is based on the fact that, with an exactly vertical lowering process, the distance between the two stay attachment points of each of the two synchronous stays remains independent of the lift position. On the other hand a movement of the crossmember from the central position in or against the direction of travel means that the distance between the stay hinge points wants to change, and that one of the distances wants to increase and another wants to decrease. However, since the stay of which the two fixing points wish to move away from each other acts against the extension, a stabilizing effect is introduced. The other stay would by contrast be compressed and cannot offer any resistance to the deflection. If the direction of the crossmember deflection changes, the effect reverses, so that the two synchronized stays alternate in stabilizing the crossmember.
In the prior art outlined above, the stay tensioning effect described produces a disadvantage which prevents the known solution from functioning correctly. The guidance of the synchronized stays over the deflection pulleys in the area of the hinging of the telescopic struts on the crossmember with deflection pulley axes arranged at right angles to the direction of travel of the crossmember means that the angle of grip on the stay deflection pulleys increases or decreases depending on the lift position of the crossmember or the angular position of the telescopic struts. Since the distances between the stay hinge points do not change the synchronized stays would have to be extended or shortened for an exact vertical lifting movement of the crossmember. This could however only be compensated for by an elasticity of the synchronized stays, e.g. by springs at the stay attachment points. Such elasticity of the stay tensioning runs contrary to the requirement for a stiff, swing-free suspension guidance however.